The invention relates to a clip for use in a knock-down structure, and more particularly but not exclusively, to a releasable plastic clip for use in securing panels of a knock-down structure, for example a collapsible container, to one another.
Containers, such as crates and boxes, (in this specification the terms will be used interchangeably) are widely used for the transportation of goods in many different industries, whilst utilizing many different modes of transportation. When carrying heavy loads, boxes are often made from wood, for example in the form of wooden sheets in the form of planks or plywood panels, which are secured to one another by means of nails, screws and tightening bands so as to form an enclosed volume
Most containers are for single use only and are discarded after the transported goods have reached their destination. This procedure is increasingly coming under pressure due to financial, environmental and safety reasons. Disassembly, reuse, removal, destruction and processing of used containers pose a number of risks for users of the containers. People can, for example, be injured in the process of disassembling a box if the box was not designed and constructed with the end goal of easy disassembly kept in mind. The processing of the materials for re-use is also time consuming and expensive, at least in part due to the fact that the constituent parts (i.e. wooden components and steel fasteners) need to be carefully separated as part of the recycling process. Furthermore, in industries where an end user receives a large number of goods and parts from suppliers, and where these products are delivered in plastic, metal or wooden containers, packaging materials can quickly pile up, which significantly increases the cost of handling and storage.
In recent times, the above concerns have led to the development and use of collapsible containers. These containers can easily be erected and assembled to form small or large containers, and this can typically be done by a single person without the use of nails, a hammer or other traditional tools and equipment associated with assembling wooden containers. Many of these wooden containers utilize a system of special clips, in which the clips are adapted securely, but releasably, to secure two adjacent wooden panels to one other. In this way, side walls of the container are connected to one other and to a base using a plurality of clips. A lid is then also securable to an opposing end of the interconnected sidewalls so as to form a complete transportation container which can be handled by a forklift.
In applications where a load to be carried by a container is significant, a clip-assembled container must still be of a design that ensures durability during all normal handling and transportation actions. This means that clips used to assemble the container must be sufficiently strong to withstand both the load carried by the box, as well as additional impact forces exerted on the dips when the box is exposed to external forces, for example when the box bounces, vibrates or are manhandled during loading, transportation and storage. Consequently the most common clips are typically made from high strength steel of 1-2 mm thickness and which are between 20 and 60 mm in width. Often clips are also heat treated to create flexible, strong spring clips.
At present, spring steel that is bent into a desired shape results in the simplest design, and therefore the lowest price in production, as only cutting, bending and surface treatment is necessary. As low complexity ensures correct function over time, producers are reluctant to introduce more complex clips where reliability may potentially be adversely affected by the increased complexity.
In order to maximize the life of these collapsible containers, it is important for the wooden panels to be maintained in a good condition. In particular, it is important for connecting grooves provided in edge zones of the wooden panels to be protected against damage and wear. This can in part be achieved by proper clip design, wherein the design should preferably be such that no sharp edges of the clips engage the grooves provided in the wooden panels when clips are secured to the wooden panels. For this reason, most clips do not have sharp free ends that directly engage the wood, but instead terminate in bent, rounded ends that allow the clip to slide safely and with reduced friction over the fragile wooden surface and locking edges without sacrificing too much clamping force. A clip of this design is shown in FIGS. 1 and 2, which illustrates a clip 100 comprising a sheet of metal having been bent at a right angle in order to define two opposing legs (101 and 102). Each leg terminates in a rounded end 103 which in use engages slots 104 provided in a wooden panel 105.
When assembled, the clips are exposed to various forces, including bending moments induced by the relative angular displacement between adjoining panels, and also shear forces resulting from relative transverse displacement of adjoining panels. This is not limited to gradual and constant loading, and additional impact loads may be exerted on the clips during handling and transportation of the box, where the box and content are subjected to impacts, shocks and vibration. The clips therefore have to be very strong, and have to exert a significant clamping force on the adjoining panels. It follows that the ends of the clips must securely engage the grooves provided in the panels.
Steel clips generally work well, but suffer from a number of disadvantages including the cost of manufacturing the clips, corrosions (in particular stress corrosion cracking), and also the weight of the steel clips. It would therefore be beneficial to develop a synthetic clip, or a clip made from recycled material, to use as an alternative or replacement to traditional steel clips. It should, however be noted that existing steel clipping systems are based on the principle of resilient clips that grip end zones of adjacent panels around a corner formed by such panels, with slots provided in the edge zones of such panels for receiving the ends of the clips. However, plastic (or another suitable synthetic or recycled material) does not exhibit a long terms spring effect, and will accordingly relax and prolong over time if continuously exposed to stress. The same design criteria used when designing steel clips can therefore not simply be applied to the design and manufacture of plastic clips, which is also a reason why there has not been much development in this area.
It is accordingly an object of the invention to provide a clip for a knock-down structure, for example a collapsible container that will, at least partially, alleviate the above disadvantages.
It is also an object of the invention to provide a plastic clip for a knock-down structure, for example a collapsible container, which will be a useful alternative to existing releasable steel clips.